In the wood working art many power operated wood working machines are employed. Included among such machines are planing machines, multi-planing machines, joiner machines, thicknessing machines, parquet strip planing machines and various other wood working machines which include elongate power driven cylindrical rotors or knife driving shafts with pluralities of circumferentially spaced longitudinally extending substantially radially outwardly projecting cutting blades or knives. The knife driving shafts in such machines are generally cylindrical and are rotated at high speed. Wood to be worked upon is guided by the machines and advanced across a plane that is substantially tangential with the shaft and extends through a cord of the circular path of the knives, whereby the knives cut and remove predetermined surface portions of the wood worked upon and establish new surfaces thereon.
Throughout the many years that the machines of the character referred to above have been in common and regular use, the basic dimensions and cross-sectional configuration of planing knives has become substantially standardized and the structural character and features of the knife driving shafts which accommodate and hold the knives have become substantially standardized. Also, the knives and the knife driving shafts are provided in a multiplicity of standard lengths. The great majority of the different available lengths of knives and shafts vary uniformly between 60 millimeters and 810 millimeters. While it is not uncommon to find non-standard (odd size and shape) planing knives and knife driving shafts with non-standard knife mounting means, such non-standard structures are generally costly custom built structures made to perform special work or are cheap, inexpensive non-industrial quality structures specially designed and produced for sale to the non-professional, non-commercial user.
The standard planing knife is established of a length of flat tool steel that is rectangular in cross-section. The standard knife has straight, flat opposite ends, flat front and rear surfaces and straight, longitudinally extending inner and outer edges. The inner edge is flat and at right angle to the front and rear surfaces and the outer edge is a flat, forwardly and outwardly inclined surface that converges with the front surface at an acute angle to define a straight, longitudinally extending forwardly and outwardly disposed cutting edge. The outer inclined surface and/or cutting edge is established by grinding and honing or otherwise dressing the outer edge portion of the knife. The knife is established of sufficiently soft tool steel so that establishing a clean and sharp cutting edge and subsequently and repeatedly resharpening that cutting edge can be performed in a most effective and efficient manner. Since soft tool steel is used to establish such a knife, the thickness thereof must be and is made substantial in order to impart the knife with sufficient strength to withstand the workloads imposed upon it.
Standard planing knife driving shafts are provided in a number of different lengths and diameters. Further, such shafts are provided to accommodate and carry different numbers of planing knives. The standard means or structure embodied in driving shafts to accommodate and hold the knives comprises longitudinally extending substantially radially outwardly opening channels machined in the shafts to accommodate the knives and to accommodate elongate screw actuated clamp bars that serve to clamp the knives in fixed position in the channels. The channels have flat, radially extending rearwardly disposed forward side surfaces and flat, substantially forwardly disposed rear side surfaces that are inclined radially outwardly and forwardly relative to the forward surfaces so that the channels are in the nature of modified dovetailed grooves. The radial extent or depth of the channels and radial extent of the knives is such that when positioned in the channels with their rear surfaces in flat supported engagement with the rear surfaces of the channels, their outer cutting edge portions project radially outward from the channels in predetermined working position relative thereto. The clamp bars fit freely within the channels and have flat rearwardly disposed clamping faces that bear against the front surfaces of the knives and the holders. The clamp bars have longitudinally spaced jack bolts or similar screw fasteners threadedly engaged in them to project forwardly therefrom to engage the front surfaces of the channels. By suitably turning the jack bolts, the bars are moved rearwardly in the channels to urge and hold the knives in tight clamped engagement against the rear surfaces of the channels. Due to the dovetailed character of the channels when the knives, bars and jack bolts are set, their radial displacement from within the channels is effectively prevented and the resulting assemblies are safe to operate.
Assembly and proper setting of the knives in the channels of the driving shafts requires the exercise of special learned skill and is a time-consuming and often difficult to perform operation. To facilitate proper setting of planing knives in related channels of related driving shafts, the prior art has equipped such shafts with screw-operated support units spaced longitudinally of the channels to occur between the bottoms of the channels and the inner bottom edges of the knives. By appropriately turning and adjusting the screw-operated support units, the radial set positions of the knives in the channels and relative to the shafts can be accurately set. Due to certain structural characteristics and dimensional limitations, the noted support units must be engaged in special large diameter holes drilled substantially radially inward into the shaft through the planes of the rear surfaces of the channels and inward from the bottoms of the channels. Accordingly, the provision and use of such support units is limited to those few large size planing knife and driving shaft assemblies which present enough stock to accommodate the required holes therefor without adversely affecting the structural integrity of the shafts.
In FIGS. 12 and 13 of the accompanying drawings which will hereinafter be described, I have illustrated a prior art structure with a support unit, such as referred to above, embodied in it.
In the recent past, the prior art has provided a novel planing knife assembly comprising an elongate knife holder that is substantially similar in dimension and configuration with a standard planing knife but which is relieved to establish a forwardly and outwardly opening recess in its outer forward portion in which a thin, flat, double-edge disposable knife of hardened steel is set so that one edge thereof projects outward from the holder. The knife holder is provided with a plurality of longitudinally spaced orienting and retaining pins that project forwardly into the recess and the double-edge disposable knife has orienting openings in and through which the pins project to properly orient and retain the knife and holder assembled. The disposable, double-edge knife and holder assembly is such that when one edge of the knife becomes dull, the knife can be easily and quickly turned over to present its other and sharp edge to perform work. The hardened steel disposable double-edge knife costs less than the cost of resharpening a standard reusable standard planing knife and each edge thereof will, as a general rule, remain effectively sharp twice as long as the cutting edge of a standard knife. Further, the disposable double-edge knife can be turned over and/or replaced in a very small fraction of the time that must be expanded merely to resharpen a standard knife.
The above noted disposable double-edge planing knife and knife holder assembly is such that it can be substituted for and used in place of a standard planing knife in a standard knife driving shaft.
In accordance with the above, it will be apparent that the noted new disposable double-edge planing knife and knife holder assembly affords great advantages over standard planing knives and constitutes a notable advance in the art.
While the above noted disposable double-edge planing knife and knife holder assembly has proven to afford many advantages over standard reusable planing knives, it has certain shortcomings which many users find extremely troublesome. The basic shortcoming found in the noted assembly is the tendency for the knife and holder to fall apart or separate during installation and adjustment of the cutting edge of the knife relative to the exterior of its related knife-driving shaft. This noted shortcoming becomes most troublesome in those instances where the knife-driving shaft is not provided with the above noted screw operated support units to orient the knife and holder assembly radially of its related shaft. In such cases, the knife and holder assembly must first be frictionally clamped in its related channel by its related clamp bar with its outer edge portions extending a substantial distance outward beyond its ultimate set position. Thereafter, the installer must carefully press and/or tap the assembly inward in the channel and relative to the shaft to desired set position. Due to the frequent inability to establish uniform pressure and frictional engagement between the several opposing bearing surfaces of the structure throughout the longitudinal extent thereof and the frequent inability to apply uniform pressure on and effect uniform sliding movement of the assembled parts, the holder and knife assembly becomes misaligned and cannot be set as desired without repeatedly releasing it and undertaking to reset it properly. It can be anticipated that one will have to release and proceed with resetting a knife and holder assembly two or three times before attaining a proper set of the outer cutting edge of the knife relative to the driving shaft.